Coating compositions exhibiting corrosion resistance properties, related coated articles and methods

ABSTRACT

Disclosed are coating compositions, such as primer compositions, suitable for providing corrosion protection to metal substrates, as well as related coated articles and methods.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is continuation of U.S. patent application Ser. No.12/108,758, entitled “Coating Compositions Exhibiting CorrosionResistance Properties, Related Coated Articles and Methods,” which wasfiled on Apr. 24, 2007, which is a continuation-in-part of U.S. patentapplication Ser. No. 11/610,069, entitled, “Coating CompositionsExhibiting Corrosion Resistance Properties, Related Coated Articles andMethods”, which was filed Dec. 13, 2006, now abandoned, and which is acontinuation-in-part of U.S. patent application Ser. No. 11/415,582,entitled, “Coating Compositions Exhibiting Corrosion ResistanceProperties, Related Coated Articles and Methods”, which was filed May 2,2006, now abandoned, all of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to coating compositions, such as primercompositions, suitable for providing corrosion protection to metalsubstrates, as well as related coated articles and methods.

BACKGROUND INFORMATION

Protection of metals from oxidation (rusting) and subsequent corrosionis often vitally important, such as, for example, when such metals areused to construct components incorporated into automotive, aerospace,architectural, and other industrial structures and parts. Variousmethods have been employed to achieve varying levels of corrosionprotection.

In some cases, a galvanization process is used to impart corrosionprotection to metallic surfaces. This process involves the hot-dip orelectroplating application onto a metal substrate of a metal filmdeposited from a metal ingot. The metal of the metal film often has agreater ionization tendency than the metal of the metal substrate. As aresult, as long as physical contact is maintained between the metal filmand the substrate, the film is theoretically preferentially oxidizedwhile the underlying substrate, which acts as an electrical conductor totransfer electrons from the metal film to oxygen, is protected.

Galvanization, however, is not ideal in all situations. For example,when utilizing hot dip galvanizing, it is difficult, if not impossible,to control the thickness of the metal film. As a result, hot dipgalvanizing is not usually suitable in cases where corrosion protectionis required for relatively small metal articles with complex shapes,such as fasteners, for example, nuts, bolts, and the like.Electroplating galvanization, on the other hand, while often enablingimproved film thickness control over hot dip galvanizing, can be anexpensive process due, for example, for the need to prevent “hydrogenembrittlement.” This phenomena is known to occur during the platingprocess, wherein hydrogen is absorbed into the coated metal article andentrapped. Subsequently, the hydrogen can cause failure. As a result,additional, costly process steps are often employed to minimize orprevent hydrogen embrittlement.

In some cases, metal substrates are protected by use ofcorrosion-resisting primer coatings that incorporate metal particles,often zinc, as a metallic pigment. These coating compositions produce acoating that utilizes the same mechanism for corrosion protection as themetal films resulting from galvanizing. Often referred to as “zinc-richprimers”, such coating compositions often outperform galvanization andare commonly applied to a metal substrate by a dip spin procedure. Thesecompositions often incorporate zinc particles, often zinc flake, as themetallic pigment in combination with an organic binder, such as an epoxyresin and/or an inorganic binder, such as a silicate.

While “zinc-rich primers” developed heretofore are suitable in manyapplications, they do have certain drawbacks that can render themdeficient in some cases. For example, to be effective, it has beenbelieved that these compositions should deposit a continuous layer ofmetallic pigment, such as zinc, onto the metal substrate. When a powder,which is relatively inexpensive, is used, it is often important to applythe composition at relatively large film thickness, usually greater than3 mils (76.2 microns), to ensure that a continuous layer of metallicpigment is deposited. The use of such thick films is, of course,undesirable from a cost standpoint. It can also render the use of suchcompositions impractical when corrosion protection is required forrelatively small metal articles with complex shapes, such as fasteners,for example, nuts, bolts, and the like.

As a result of this perceived deficiency, metal flakes, such as zincflakes, are often used as the metallic pigment in zinc-rich primercompositions. The use of these thin, plate-like structures, can resultin the deposition of a continuous film of metallic pigment, even whenthe composition is deposited at a relatively low film thickness, evenbelow 1 mil (25.4 microns). The nature of these materials, however,often causes the resultant coating to exhibit poor adhesion to a metalsubstrate as well as subsequently applied coatings. Thus, up to four dipapplications of a solvent based colored coating composition is oftenapplied over the primer (black is often a desired color). Moreover,aqueous based, electrodepositable coating compositions, which are oftendesirable for use as corrosion inhibiting coating compositions, often donot adhere to zinc-rich primers that rely on the use of commercial zincflakes.

A disadvantage that has been observed in the use of inorganic binders inzinc-rich primer compositions is that they tend to be brittle and,therefore, the resulting zinc-rich primer composition can be powdery andexhibit poor adhesion to the metal substrate. This deficiency isparticularly problematic when attempting to coat small parts, such asfasteners, which are handled in bulk. In this process, the parts oftencontact one another. As a result, when a brittle, poorly adhered film isapplied to the parts, the film is easily damaged when the parts contactone another during the coating process. This damage leads to poorcorrosion resistance performance.

As a result, it would be desirable to provide coating compositions thatcan impart desirable levels of corrosion protection to metal substrateseven when applied at relatively low film thickness. Moreover, it wouldbe desirable to provide such coating compositions that are flexible andadhere well to metal substrates as well as a subsequently appliedaqueous electrodepositable coating compositions, to provide a desiredcolor and a desirable level of corrosion protection to a metal article,such as small metal parts with complex shapes, such as fasteners, forexample, nuts, bolts, and the like.

As previously mentioned, small metal parts, such as those mentionedabove, are often handled in bulk during the coating process. In otherwords, many parts are coated simultaneously in a coating apparatus. Inmany instances, as indicated earlier, the individual parts come on closeproximity to or contact each other while passing through the coating anddrying systems such that when the coating is applied over the parts anddried or cured, two or more parts may adhere together at the point ofengagement (often referred to as a “touch point”). These coated partsmust then be separated from each other with some degree of force that,typically, results in the removal of at least some of the coating fromeach of the parts at or around the touch point. If a light,silver-colored (as is common) zinc-rich primer has been deposited undera dark, often black-colored (as is common) electrodeposited coating,removal of the dark electrodeposited coating will reveal the presence ofthe light undercoating, which is often unsightly and undesirable. As aresult, it would be desirable to provide zinc rich coatings that havethe flexibility and adhesion characteristics described above and whichare dark in color, such as black, so that they exhibit a color similarto that of a subsequently applied electrodeposited coating.

SUMMARY OF THE INVENTION

In certain respects, the present invention is directed to dark-coloredcoating compositions comprising: (a) dark-colored metal particles, and(b) a film-forming binder comprising a hybrid organic-inorganiccopolymer formed from: (1) a titanate and/or a partial hydrolysatethereof; and (2) a polyfunctional polymer having functional groupsreactive with alkoxy groups of the titanate and/or partial hydrolysatethereof.

In other respects, the present invention is directed to dark-coloredzinc-rich coating compositions comprising: (a) at least 25 percent byweight, based on the total solids weight of the composition, ofdark-colored zinc flakes; and (b) a binder formed from a titanate.

In still other respects, the present invention is directed to metalarticles at least partially coated with a multi-component compositecoating comprising: (a) a dark-colored zinc-rich primer coating; and (b)a dark-colored electrodeposited coating deposited over at least aportion of the zinc-rich primer coating. These articles of the presentinvention are resistant to corrosion after 500 hours of exposure, whenthe total combined dry film thickness of the zinc-rich primer and theelectrodeposited coating is no more than 1.5 mils (38.1 microns).

The present invention is also directed to methods for coating metalarticles. These methods comprise: (a) depositing a dark-coloredzinc-rich primer coating over at least a portion of a surface of thearticle, wherein the zinc-rich primer coating is deposited from acomposition comprising: (1) at least 25 percent by weight, based on thetotal solids weight of the composition, of dark-colored zinc particles;and (b) a binder formed from a titanate; and (b) electrodepositing adark-colored coating over at least a portion of the zinc-rich primercoating. In some embodiments, the total combined dry film thickness ofthe zinc-rich primer and the electrodeposited coating is no more than1.5 mils (38.1 microns).

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1a and 1b are cross-sectional and surface scanning electronmicrograph (“SEM”) images (approximately 1000× magnification),respectively, of the coated substrate prepared in Example 15;

FIGS. 2a and 2b are cross-sectional and surface SEM images(approximately 1000× magnification), respectively, of the coatedsubstrate prepared in Example 16; and

FIGS. 3a and 3b are cross-sectional and surface SEM images(approximately 1000× magnification), respectively, of the coatedsubstrate prepared in Example 17.

DETAILED DESCRIPTION OF THE INVENTION

For purposes of the following detailed description, it is to beunderstood that the invention may assume various alternative variationsand step sequences, except where expressly specified to the contrary.Moreover, other than in any operating examples, or where otherwiseindicated, all numbers expressing, for example, quantities ofingredients used in the specification and claims are to be understood asbeing modified in all instances by the term “about”. Accordingly, unlessindicated to the contrary, the numerical parameters set forth in thefollowing specification and attached claims are approximations that mayvary depending upon the desired properties to be obtained by the presentinvention. At the very least, and not as an attempt to limit theapplication of the doctrine of equivalents to the scope of the claims,each numerical parameter should at least be construed in light of thenumber of reported significant digits and by applying ordinary roundingtechniques.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the invention are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contains certainerrors necessarily resulting from the standard variation found in theirrespective testing measurements.

Also, it should be understood that any numerical range recited herein isintended to include all sub-ranges subsumed therein. For example, arange of “1 to 10” is intended to include all sub-ranges between (andincluding) the recited minimum value of 1 and the recited maximum valueof 10, that is, having a minimum value equal to or greater than 1 and amaximum value of equal to or less than 10.

In this application, the use of the singular includes the plural andplural encompasses singular, unless specifically stated otherwise. Inaddition, in this application, the use of “or” means “and/or” unlessspecifically stated otherwise, even though “and/or” may be explicitlyused in certain instances.

Certain embodiments of the present invention are directed to coatingcompositions that comprise metal particles. The metal particlesincorporated into the coating compositions of the present invention areselected to have a greater ionization tendency than that of the metalsubstrate to which the composition is to be applied. Thus, as is oftenthe case, when the metal substrate is iron or an iron alloy, such assteel, the metal particles will typically comprise zinc particles,aluminum particles, zinc-aluminum alloy particles, or a mixture thereof.In some cases, the purity of the metal particles is at least 94% byweight, such as at least 95% by weight.

In certain embodiments, the coating compositions of the presentinvention are zinc-rich primer compositions. As used herein, the term“zinc-rich primer composition” refers to compositions comprising zincparticles, such as zinc powder, zinc dust, and/or zinc flake, which arepresent in the composition in an amount of at least 50 percent byweight, in many cases at least 70 percent by weight, such as 70 to 95percent by weight, or, in some cases, 85 to 95 percent by weight, withthe weight percents being based on the total weight of solids in thecomposition, i.e., the dry weight of the composition.

The particle size of the metal particles, such as zinc particles, canvary. In addition, the shape (or morphology) of the particles, such aszinc particles, can vary. For example, generally spherical morphologiescan be used, as well as particles that are cubic, platy, or acicular(elongated or fibrous). In some cases, the metal particles comprise“metal powder”, which, as used herein, refers to generally sphericalparticles having an average particle size of no more than 20 microns,such as 2 to 16 microns. In some cases, the metal particles comprise“metal dust”, which, as used herein, refers to metal powder, such aszinc powder, having an average particle size of 2 to 10 microns. In somecases, metal particles comprise metal flakes, such as zinc flakes,which, as used herein, refers to particles having a different aspectratio than powder or dust (i.e., not a generally spherical structure)and having an elongated dimension of up to 100 microns. In some cases,mixtures of metal powder, dust, and/or flakes are used.

In certain embodiments, the metal particles utilized in the coatingcompositions of the present invention comprise zinc powder and/or zincdust. In certain embodiments, zinc powder is present in an amount of atleast 25 percent by weight, such as at least 50 percent by weight, insome cases at least 80 percent by weight, and, in yet other cases, atleast 90 percent by weight, based on the total weight of the metalparticles in the coating composition.

Moreover, in certain embodiments, the coating compositions of thepresent invention are substantially free or, in some cases, completelyfree of zinc flakes. As used herein, the term “substantially free” meansthat the material being discussed is present, if at all, as anincidental impurity. In other words, the material does not effect theproperties of another substance. As used herein, the term “completelyfree” means that the material is not present in another substance atall.

In certain embodiments, the coating compositions of the presentinvention comprise metal flakes comprising zinc alloy particles, such aszinc/aluminum and/or zinc/tin alloys, among others. Such materials,which are suitable for use in the present invention, are described inUnited States Published Patent Application No. 2004/0206266 at [0034] to[0036], the cited portion of which being incorporated herein byreference. Indeed, the inventors have surprisingly discovered that theaddition of zinc-tin alloy particles in relatively small amounts, i.e.,no more than 10 percent by weight, based on the total weight of solidsin the composition, can result in significant improvement in thecorrosion-resisting properties of certain coating compositions describedherein. Such materials are commercially available from, for example,Eckart-Werke as STAPA 4 Zn Sn 15.

As indicated, certain embodiments of the present invention are directedto “dark-colored” coating compositions. As used herein, “dark” or“dark-colored” refers to materials that are black as well as materialshaving a color approaching black in hue, including, for example, darkgrey, dark blue, dark green, dark brown, and the like. As used herein,“black” includes all dark, optically black colors. The term “opticallyblack” refers herein to a material which appears black and opaque onvisual inspection. In certain embodiments, the dark-colored coatingcompositions of the present invention are optically black.

In certain embodiments, the dark-colored coating compositions of thepresent invention are capable of producing a coating having a CIELAB L*value of no more than 60, such as no more than 50, or, in some cases, nomore than 40. For purposes of the present invention, the L* value for amaterial is found as measured at an angle of 45° using an X-Rite MA-68available from X-Rite, Incorporated, Grandville, Mich. The X-Rite MA-68instrument measures according to the L*a*b color space theory. TheL*a*b* color space theory states that every color can be plotted in athree dimensional space, with the lightness and darkness on the “L”(verticle) axis, the reds and greens on the “a” (left to right) axis andthe yellows and blues on the “b” (front to back) axis. Forlightness-darkness, measurements are made with particular reference tothe L* values of the L*a*b* coordinates.

The dark-colored, sometimes optically black, coating compositions of thepresent invention comprise dark-colored metal particles. As used herein,the term “dark-colored metal particles” refers to metal particles, suchas those described above, which themselves are dark-colored as definedabove, sometimes optically black. In certain embodiments, thedark-colored metal particles themselves have a CIELAB L* value of nomore than 60, such as no more than 50, or, in some cases, no more than40. In other words, the metal particles are such that, and are presentin an amount sufficient to, cause the resultant coating composition tobe a dark-colored coating composition as defined above.

In certain embodiments, the dark-colored metal particles comprise blackzinc flakes, such as those commercially available as Blitz® Z2031 fromBenda-Lutz Corporation, Independence, Ky. Indeed, it has beensurprisingly discovered that the inclusion of such black zinc flakesdoes not detrimentally impact the ability of certain coatingcompositions of the present invention to adhere to subsequently appliedaqueous based electrodepositable coating compositions, unlike as isoften the case with other zinc flakes, as mentioned earlier.Particularly significant improvement in such adhesion has been foundwhen the dry film thickness of the zinc-rich primer is at least 0.5 mils(12.7 microns), more particularly at least 0.7 mils (17.8 microns) orhigher. As a result, the dark-colored coating compositions of thepresent invention are suitable for preparing metal articles at leastpartially coated with a multi-component composite coating comprising:(a) a dark-colored zinc-rich primer coating; and (b) a dark-coloredelectrodeposited coating deposited over at least a portion of thezinc-rich primer coating, wherein the article is resistant to corrosionafter 500 hours of exposure when the total combined dry film thicknessof the zinc-rich primer and the electrodeposited coating is no more than1.5 mils (38.1 microns) and, in some cases, at least 1 mil (25.4microns).

In certain embodiments, the dark-colored metal particles are present inan amount of at least 25 percent by weight, such as at least 50 percentby weight, in many cases at least 70 percent by weight, such as 70 to 95percent by weight, or, in some cases, 85 to 95 percent by weight, withthe weight percents being based on the total weight of solids in thecomposition, i.e., the dry weight of the composition.

The coating compositions of the present invention also comprise abinder, such as a film-forming binder. As used herein, the term “binder”refers to a material in which the metal particles are distributed andwhich serves to bond the coating composition to either a bare orpreviously coated substrate, such as a metal substrate. As used herein,the term “film-forming binder” refers to a binder that forms aself-supporting, substantially continuous film on at least a horizontalsurface of a substrate upon removal of diluents and/or carriers that maybe present in the composition.

In certain embodiments, the film-forming binder present in the coatingcompositions of the present invention comprises a hybridorganic-inorganic copolymer. As used herein, the term “copolymer” refersto a material created by polymerizing a mixture of two or more startingcompounds. As used herein, the term “hybrid organic-inorganic copolymer”refers to a copolymer with inorganic repeating units and organicrepeating units. For purposes of the present invention, the term“organic repeating units” is meant to include repeating units based oncarbon and/or silicon (even though silicon is not normally considered anorganic material), while the term “inorganic repeating units” is meantto refer to repeating units based on an element or elements other thancarbon or silicon.

In certain embodiments, the film-forming binder utilized in certainembodiments of the coating compositions of the present invention isformed from a titanate and/or a partial hydrolysate thereof. As usedherein, the term “titanate” refers to a compound comprising four alkoxygroups, which compound is represented by the formula Ti(OR)₄, whereineach R is individually a hydrocarbyl radical containing from, forexample, 1 to 10, such as 1 to 8, or, in some cases 2 to 5 carbon atomsper radical, such as, for example, alkyl radicals, cycloalkyl radicals,alkylenyl radicals, aryl radicals, alkaryl radicals, aralkyl radicals,or combinations of two or more thereof, i.e., each R can be the same ordifferent. Such materials, which are suitable for use in the presentinvention, are described in U.S. Pat. No. 6,562,990 at col. 4, line 63to col. 5, line 9, the cited portion of which being incorporated hereinby reference. Commercially available materials, which are examples oftitanates that are suitable for use in the present invention, are theproducts sold by DuPont under the tradename TYZOR®, such as TYZOR TPT,which refers to tetraisopropyl titanate, TYZOR TnBT, which refers totetra-n-butyl titanate, and TYZOR TOT, and which refers totetra-2-ethylhexyl titanate.

In certain embodiments, the titanate used in preparing the film-formingbinder utilized in certain embodiments of the coating compositions ofthe present invention is a chelated titanate. Suitable chelatedtitanates include, but are not limited to, products commerciallyavailable from DuPont under the TYZOR tradename. Suitable chelatedtitanates also include, but are not limited to, the chelated titanatesdescribed in U.S. Pat. Nos. 2,680,108 and 6,562,990, which areincorporated herein by reference. In certain embodiments of the presentinvention, a chelated titanate is used that is formed from the use of achelating agent comprising a dicarbonyl compound. Dicarbonyl compoundsthat are suitable for use in preparing the titanium chelate utilized asa binder in certain embodiments of the coating compositions of thepresent invention include, but are not limited to, the materialsdescribed in U.S. Pat. No. 2,680,108 at col. 2, lines 13-16 and U.S.Pat. No. 6,562,990 at col. 2, lines 56-64.

In certain embodiments of the present invention, the film-forming binderis formed from the reaction of a titanate and/or a partial hydrolysatethereof, such as any of the titanates and/or chelated titanatespreviously described, and a polyfunctional polymer comprising functionalgroups reactive with alkoxy groups of the titanate and/or a partialhydrolysate thereof. As used herein, the term “polymer” is meant toinclude oligomers and both homopolymers and copolymers. Suitablepolymers include, for example, acrylic polymers, polyester polymers,polyurethane polymers, polyether polymers and silicon-based polymers,i.e., polymers comprising one or more —SiO— units in the backbone. Asused herein, the term “polyfunctional polymer” is meant to refer topolymers having at least two functional groups. As used herein, thephrase “formed from” denotes open, e.g., “comprising,” claim language.As such, a composition or substance “formed from” a list of recitedcomponents refers to a composition or substance comprising at leastthese recited components, and can further comprise other, non-recitedcomponents, during the composition or substance's formation.

As indicated, the polyfunctional polymer utilized in the preparation ofthe film-forming binder of certain embodiments of the coatingcompositions of the present invention comprises two or more functionalgroups reactive with alkoxy groups of the titanate and/or partialhydrolysate thereof. Examples of such functional groups are hydroxylgroups, thiol groups, primary amine groups, secondary amine groups, andacid (e.g. carboxylic acid) groups, as well as mixtures thereof.

In certain embodiments, the polyfunctional polymer utilized in thepreparation of the film-forming binder of certain embodiments of thecoating compositions of the present invention comprises a polyhydroxycompound, i.e., a polyol. As used herein, the terms “polyhydroxycompound” and “polyol” refers to materials having an average of two ormore hydroxyl groups per molecule. Suitable polyols include, but are notlimited to, those described in U.S. Pat. No. 4,046,729 at col. 7, line52 to col. 10, line 35, the cited portion of which being incorporated byreference.

In certain embodiments of the present invention, the polyol is formedfrom reactants comprising (i) a polyol, such as a diol (a materialhaving two hydroxyl groups per molecule), comprising an aromatic groupand (ii) an alkylene oxide. In these embodiments, the aromatic groupcontaining polyol, such as a diol, may include one or more aromaticrings, and if more than one ring is present, the rings can be fusedand/or unfused. Examples of aromatic group containing diols, which aresuitable for use in the present invention, are bisphenols, such asBisphenols A, F, E, M, P and Z. In these embodiments, the polyolundergoes chain extension by reaction with an alkylene oxide. Thealkylene moiety of the alkylene oxide can have any number of carbonatoms, and can be branched or unbranched. Examples of suitable, butnon-limiting, alkylene oxides are those having from 1 to 10 carbonatoms, such as those having 2 to 4 carbon atoms. Such compounds arewidely commercially available.

In these embodiments, the polyol can be reacted with the alkylene oxidein any suitable molar ratio. For example, the ratio of aromatic diol tothe alkylene oxide can be from 1:1 to 1:10, or even higher. Standardreaction procedures can be used to react the alkylene oxide to one ormore of the hydroxyl groups of the polyol, and to further link thealkylene oxide groups to each other for additional chain extension.Alternatively, suitable materials are commercially available, such asfrom BASF, in their MACOL line of products. One suitable product is amaterial in which six moles of ethylene oxide are reacted with one moleof Bisphenol A, commercially available as MACOL 98B.

As a result, as will be apparent from the foregoing description, thefilm-forming binder utilized in certain embodiments of the coatingcompositions of the present invention comprises a structure representedby the general formula:

wherein P is the residue of a polyfunctional polymer, such as a polyol,such as a polyol formed from the reaction of a polyol comprising anaromatic group and an alkylene oxide; and each n is an integer have avalue of 1 or more, such as 1 to 10, or, in some cases, n is 1, and eachn may be the same or different. As will be appreciated, to obtain astructure as previously described wherein n is greater than 1, water maybe added to the titanate to form a partial hydrolysate. This can beaccomplished prior to addition of a polyfunctional polymer, with thepolyfunctional polymer, or after the addition of the polyfunctionalpolymer. Otherwise, commercially available partial hydrolysates, such asTYZOR BTP (n-butyl polytitanate), can be used.

The Examples herein illustrate suitable methods for producing afilm-forming binder utilized in certain embodiments of the coatingcompositions of the present invention. In certain embodiments, such abinder is produced by reacting a titanate and a polyfunctional polymerat a weight ratio of from 1 to 6, such as 3 to 5, parts by weighttitanate, measured on the basis of theoretical TiO₂ content in theresulting binder, to 1 part by weight of the polyfunctional polymer.Indeed, it has been surprisingly discovered that use of a film-formingbinder comprising the hybrid organic-inorganic copolymer formed fromsuch a reaction can produce zinc-rich primer compositions wherein theamount of organic material is minimized, while still obtaining desirablefilm properties due to, it is believed, the presence of the organicrepeating units. It is believed that this minimization of organicspecies is beneficial because such species can act as an insulatorbetween zinc particles, thereby reducing their sacrificial activity. Itis also believed that the minimization of organic species in thecompositions of the present invention can render such compositionsparticularly suitable for use on metal parts that are intended to beutilized in relatively high temperature applications, where such organicspecies may degrade, such as, for example, automobile mufflers and thelike.

In certain embodiments, the film-forming binder is present in thecoating compositions of the present invention in an amount of 2 to 10percent by weight, such as 3 to 7 percent by weight, with the weightpercents being based on the total weight of solids in the composition,i.e., the dry weight of the composition.

The coating compositions of the present invention may include othermaterials, if desired. For example, in certain embodiments, the coatingcompositions of the present invention comprise a diluent so that thecomposition will have a desired viscosity for application byconventional coating techniques. Suitable diluents include, but are notlimited to, alcohols, such as those having up to about 8 carbon atoms,such as ethanol and isopropanol and alkyl ethers of glycols, such as1-methoxy-2-propanol, and monoalkyl ethers of ethylene glycol,diethylene glycol and propylene glycol; ketones, such as methyl ethylketone, methyl isobutyl ketone and isophorone; esters and ethers, suchas 2-ethoxyethyl acetate and 2-ethoxyethanol; aromatic hydrocarbons,such as benzene, toluene, and xylene; and aromatic solvent blendsderived from petroleum, such as those sold commercially under thetrademark SOLVESSO®. The amount of diluent will vary depending on themethod of coating, the binder component, the metal particles to binderratio, and the presence of optional ingredients such as those mentionedbelow.

In addition to the ingredients described above, the coating compositionsof the present invention may contain, for example, a secondary resin, athickener, a thixotropic agent, a suspension agent, and/or a hygroscopicagent, including those materials described in U.S. Pat. No. 4,544,581 atcol. 3, line 30 to col. 4, lines 64, the cited portion of which beingincorporated herein by reference. Other optional materials includeextenders, for example, iron oxides and iron phosphides, flow controlagents, for example, urea-formaldehyde resins, and/or dehydratingagents, such as silica, lime or a sodium aluminum silicate.

In certain embodiments, other pigments may be included in thecomposition, such as carbon black, magnesium silicate (talc), and zincoxide. In certain embodiments, the coating compositions of the presentinvention also include an organic pigment, such as, for example, azocompounds (monoazo, di-azo, (β-Naphthol, Naphthol AS, azo pigment lakes,benzimidazolone, di-azo condensation, metal complex, isoindolinone,isoindoline), and polycyclic (phthalocyanine, quinacridone, perylene,perinone, diketopyrrolo pyrrole, thioindigo, anthraquinone, indanthrone,anthrapyrimidine, flavanthrone, pyranthrone, anthanthrone, dioxazine,triarylcarbonium, quinophthalone) pigments, as well as mixtures thereof.

The coating compositions of the present invention are substantially freeor, in some cases, completely free, of heavy metals, such as chrome andlead. As a result, certain embodiments of the present invention aredirected to “chrome-free” coating compositions, i.e., compositions thatdo not include chrome-containing substances.

One advantage of certain embodiments of the coating compositions of thepresent invention is that, unlike many prior art zinc rich primercompositions, they may be embodied as a single component, i.e.,one-package, coating composition. As a result, the coating compositionsof certain embodiments of the present invention can be easily prepared,stored, and transported.

The coating compositions of the present invention may be applied to asubstrate by any of a variety of typical application methods, such asimmersion, including dip drain and dip-spin procedures (after dipping,the article is spun in order to scatter any excess coating material bycentrifugal force), curtain coating, rolling, brushing or sprayingtechniques.

Any article may be coated with the coating compositions of the presentinvention, such as, for example, those that are constructed of ceramicsor plastics. In many cases, however, the article is a metal article and,as a result, the coating compositions are, in these embodiments, appliedto a metal substrate, such as a zinc or iron containing substrate, e.g.,a steel substrate. As used herein, the term “zinc substrate” refers to asubstrate of zinc or zinc alloy, or a metal such as steel coated withzinc or zinc alloy, as well as a substrate containing zinc inintermetallic mixture. Likewise, the iron of the substrate can be inalloy or intermetallic mixture form.

In certain embodiments, the metal article to be coated with a coatingcomposition of the present invention is a “small part”. As used herein,the term “small part” is meant to include (i) fasteners, such as nuts,bolts, screws, pins, nails, clips, and buttons, (ii) small sizestampings, (iii) castings, (iv) wire goods, and (v) hardware. In certainembodiments, the small part is a fastener to be used in an automotiveand/or aerospace application.

In certain embodiments, such metal substrates comprise a bare uncoatedor untreated surface. In other cases, however, the coating compositionsof the present invention are applied to a metal substrate that hasalready been coated, such as with a chromate or phosphate pretreatment.In some cases, the substrate may be pretreated to have, for example, aniron phosphate coating in an amount from 50 to 100 mg/ft² or a zincphosphate coating in an amount from 200 to 2,000 mg/ft².

The coating compositions of the present invention may be deposited ontothe substrate at any desired film thickness. In many cases, however,relatively thin films, i.e., dry film thickness of no more than 0.5 mils(12.7 microns), in some cases no more than 0.2 mils (5.1 microns), aredesirable. For purposes of the present invention, the dry film thicknessof a coating or combination of coatings is to be measured by theeddy-current principle (ASTM B244) using, for example a FISHERSCOPE® MMSthicknessmeter, manufactured by Fisher Instruments, using theappropriate probe for the material of the coated substrate.

In certain embodiments, the coating compositions of the presentinvention are made and deposited in such a manner so as to produce aporous coating, such as a zinc rich coating, comprising non-sphericalmetal particles. It has been surprisingly discovered that when such aporous coating is deposited onto a metal substrate, either a bare metalsubstrate or a pretreated metal substrate, as described earlier, theability of the coating to adhere to a subsequently applied coating, suchas an electrodeposited coating, as described below, is dramaticallyimproved while the corrosion resistance properties are not detrimentallyeffected and, in some cases, may actually be improved. In certainembodiments, the adhesion of the porous coating to a subsequentlyapplied coating is improved to such an extent that the resultingmulti-component composite coating is resistant to corrosion when testedin accordance with ASTM B117 after 500 hours of exposure or, in somecases 700 hours of exposure, or, in yet other cases, 1000 hours ofexposure, as described in more detail below.

As used herein, the term “porous coating” refers to a coating that has adiscontinuous surface that is permeable to another coating composition,such as an electrodeposited coating composition, that is applied overthe porous coating. In other words, a porous coating contains pathwayssufficient to allow the subsequently applied coating composition to atleast partially penetrate beneath the exterior surface of the porouscoating. In certain embodiments, as illustrated in the Examples herein,such pathways are visible when viewing a scanning electron micrograph(approximately 1000× magnification) of a cross-section of the porouscoating.

It has been discovered that such a porous coating can be made be aprocess comprising: (a) preparing a composition comprising: (i)generally spherical metal particles, (ii) a film-forming binder; and(iii) a solvent; and (b) converting at least some, preferablysubstantially all, of the generally spherical particles to non-sphericalmetal particles in the presence of the binder and the diluent. As usedherein, the term “substantially all” means that the amount of generallyspherical particles remaining in the composition after the convertingstep is not sufficient enough to detrimentally affect the performance ofthe resulting porous coating.

As used herein, the term “non-spherical particles” refers to particlesthat are not generally spherical, i.e., they have an aspect ratiogreater than one, in some cases the aspect ratio is 2 or higher. Withoutbeing bound by any theory, it is believed that the process of thepresent invention results in the conversion of generally spherical metalparticles to non-spherical metal particles having a variety of aspectratios and sizes, such that when the composition is deposited on asubstrate at the relatively thins film described herein, i.e., no morethan 0.5 mils, a porous coating can result, as seen in the Examples.Conversely, as is also apparent in the Examples, if conventional zincflake is used, such as Zinc 8 paste available from Eckart-America., thezinc flake particles orient themselves so as to form a non-porouscoating having a continuous and relatively smooth exterior surface,perhaps due to the relatively uniform and large aspect ratios exhibitedby such particles.

In accordance with the previously described process of the presentinvention, a composition comprising (i) generally spherical metalparticles, (ii) a binder; and (iii) a diluent is prepared. In certainembodiments, such a composition is a composition of the presentinvention described herein, wherein the generally spherical metalparticles comprise a metal having a greater ionization tendency thanthat of the metal substrate to which the composition is to be applied,as previously described, the binder comprises a hybrid organic-inorganiccopolymer formed from: (a) a titanate and/or a partial hydrolysatethereof; and (b) a polyfunctional polymer having functional groupsreactive with alkoxy groups of the titanate and/or the partialhydrolysate thereof, as previously described, and the diluent comprisesone or more of the diluents previously described.

In these processes of the present invention, at least some, preferablysubstantially all, of the generally spherical particles are converted tonon-spherical metal particles in the presence of the binder and thediluent. Any suitable technique may be used to accomplish theconversion, however, in some embodiments, a milling process, such as isdescribed in the Examples, is used. In certain embodiments, this millingis carried out in a media mill using balls (constructed of, for example,zirconium ceramic) of 0.5 to 3.0 millimeters in diameter. In some cases,a media milling process in which the mill is loaded with balls in anamount of from 50 to 60% of the mill's internal volume is used. In somecases, a media milling process in which the composition comprising thegenerally spherical metal particles occupies from 50 to 75% of themill's internal volume is used. Cooling may be provided to maintaininternal temperature in the media mill of less than 140° F., such asbelow 110° F. Milling time varies depending upon the type and size ofmill used but often ranges form 2 to 15 hours. In certain embodiments,the milling process is considered complete by comparing visualappearance of drawdowns on flat steel panels with standards generatedfrom a previous acceptable material.

Another advantage that has been discovered with respect to the foregoingprocess is that the milling process can be conducted in the substantialor complete absence of conventional lubricants, such as higher fattyacids, including stearic acid and oleic acid. It is believed, withoutbeing bound by any theory, that the presence of such lubricants candetrimentally affect the ability of the resulting coating to adhere tosubsequently applied coatings. As a result, in certain embodiments, theprocesses of the present invention comprise converting generallyspherical metal particles into non-spherical metal particles in thesubstantial absence or, in some cases, complete absence of mineralspirits, a long chain fatty acid, such as stearic acid and oleic acid, afluorocarbon resin, small pieces of aluminum foil, and/or any otherconventional lubricant.

In certain embodiments, another coating is deposited over at least aportion of the previously described coating. In particular, in certainembodiments of the present invention, an electrodepositable coatingcomposition is deposited over at least a portion of the previouslydescribed coating by an electrodeposition process.

Any suitable electrodeposition process and electrodepositable coatingcomposition may be used in accordance with the present invention. Aswill be appreciated by those skilled in the art, in the process ofapplying an electrodepositable coating composition, an aqueousdispersion of the composition is placed in contact with an electricallyconductive anode and cathode. Upon passage of an electric currentbetween the anode and cathode, an adherent film of theelectrodepositable composition deposits in a substantially continuousmanner on the substrate serving as either the anode or the cathodedepending on whether the composition is anionically or cationicallyelectrodepositable.

In certain embodiments, the electrodepositable coating compositioncomprises a resinous phase dispersed in an aqueous medium. The resinousphase includes a film-forming organic component which can comprise ananionic film-forming organic component or a cationic film-formingorganic component. In certain embodiments, the electrodepositablecoating composition comprises an active hydrogen group-containing ionicresin and a curing agent having functional groups reactive with theactive hydrogens of the ionic resin.

Non-limiting examples of anionic electrodepositable coating compositionsinclude those comprising an ungelled, water-dispersibleelectrodepositable anionic film-forming resin. Examples of film-formingresins suitable for use in anionic electrodeposition coatingcompositions are base-solubilized, carboxylic acid containing polymers,such as the reaction product or adduct of a drying oil or semi-dryingfatty acid ester with a dicarboxylic acid or anhydride; and the reactionproduct of a fatty acid ester, unsaturated acid or anhydride and anyadditional unsaturated modifying materials which are further reactedwith polyol. Also suitable are the at least partially neutralizedinterpolymers of hydroxy-alkyl esters of unsaturated carboxylic acids,unsaturated carboxylic acid and at least one other ethylenicallyunsaturated monomer. Yet another suitable electrodepositable anionicresin comprises an alkyd-aminoplast vehicle, i.e., a vehicle containingan alkyd resin and an amine-aldehyde resin. Yet another anionicelectrodepositable resin composition comprises mixed esters of aresinous polyol. These compositions are described in detail in U.S. Pat.No. 3,749,657 at col. 9, line 1 to col. 10, line 13, the cited portionof which being incorporated herein by reference.

By “ungelled” is meant that the polymer is substantially free ofcrosslinking and has an intrinsic viscosity when dissolved in a suitablesolvent. The intrinsic viscosity of a polymer is an indication of itsmolecular weight. A gelled polymer, since it is of essentiallyinfinitely high molecular weight, will have an intrinsic viscosity toohigh to measure.

A wide variety of cationic polymers are known and can be used in thepresent invention so long as the polymers are “water dispersible,” i.e.,adapted to be solubilized, dispersed, or emulsified in water. The waterdispersible resin is cationic in nature, that is, the polymer containscationic functional groups to impart a positive charge. Often, thecationic resin also contains active hydrogen groups.

Non-limiting examples of suitable cationic resins are onium saltgroup-containing resins, such as ternary sulfonium salt group-containingresins and quaternary phosphonium salt-group containing resins, forexample, those described in U.S. Pat. Nos. 3,793,278 and 3,984,922,respectively. Other suitable onium salt group-containing resins includequaternary ammonium salt group-containing resins, for example, thosethat are formed from reacting an organic polyepoxide with a tertiaryamine salt, as described in U.S. Pat. Nos. 3,962,165; 3,975,346; and4,001,101. Also suitable are amine salt group-containing resins, such asthe acid-solubilized reaction products of polyepoxides and primary orsecondary amines such as those described in U.S. Pat. Nos. 3,663,389;3,984,299; 3,947,338 and 3,947,339.

In certain embodiments, the above-described salt group-containing resinsare used in combination with a blocked isocyanate curing agent. Theisocyanate can be fully blocked, as described in U.S. Pat. No.3,984,299, or the isocyanate can be partially blocked and reacted withthe resin backbone, such as is described in U.S. Pat. No. 3,947,338.

Also, one-component compositions as described in U.S. Pat. No. 4,134,866and DE-OS No. 2,707,405 can be used as the cationic resin. Besides theepoxy-amine reaction products, resins can also be selected from cationicacrylic resins such as those described in U.S. Pat. Nos. 3,455,806 and3,928,157. Also, cationic resins which cure via transesterification,such as described in European Application No. 12463, can be used.Further, cationic compositions prepared from Mannich bases, such asdescribed in U.S. Pat. No. 4,134,932, can be used. Also useful arepositively charged resins that contain primary and/or secondary aminegroups, such as is described in U.S. Pat. Nos. 3,663,389; 3,947,339; and4,115,900.

In certain embodiments, the cationic resin is present in theelectrodepositable coating composition in amounts of 1 to 60 weightpercent, such as 5 to 25 weight percent, with the weight percents beingbased on total weight of the composition.

As previously discussed, the electrodepositable coating compositionswhich are useful in the present invention often further comprise acuring agent which contains functional groups which are reactive withthe active hydrogen groups of the ionic resin. Suitable aminoplastresins, which are often used as curing agents for anionicelectrodepositable coating compositions, are commercially available fromAmerican Cyanamid Co. under the trademark CYMEL® and from MonsantoChemical Co. under the trademark RESIMENE®. In certain embodiments, theaminoplast curing agent is utilized in conjunction with the activehydrogen containing anionic electrodepositable resin in amounts rangingfrom 5 to 60 percent by weight, such as 20 to 40 percent by weight,based on the total weight of the resin solids in the electrodepositablecoating composition.

Blocked organic polyisocyanates are often used as curing agents forcationic electrodepositable coating compositions and may be fullyblocked or partially blocked, as described above. Specific examplesinclude aromatic and aliphatic polyisocyanates, including cycloaliphaticpolyisocyanates, such as diphenylmethane-4,4′-diisocyanate (MDI), 2,4-or 2,6-toluene diisocyanate (TDI), including mixtures thereof,p-phenylene diisocyanate, tetramethylene and hexamethylenediisocyanates, dicyclohexylmethane-4,4′-diisocyanate, isophoronediisocyanate, mixtures of phenylmethane-4,4′-diisocyanate andpolymethylene polyphenylisocyanate, as well as higher polyisocyanates,such as triisocyanates, and isocyanate prepolymers with polyols such asneopentyl glycol and trimethylolpropane and with polymeric polyols suchas polycaprolactone diols and triols (NCO/OH equivalent ratio greaterthan 1). The polyisocyanate curing agents are often utilized inconjunction with the cationic resin in amounts ranging from 1 to 65percent by weight, such as 5 to 45 percent by weight, based on theweight of the total resin solids in the coating composition.

The electrodepositable coating compositions utilized in the presentinvention are typically in the form of an aqueous dispersion. The term“dispersion” refers to a two-phase transcoating, translucent or opaqueresinous system in which the resin is in the dispersed phase and thewater is in the continuous phase. The resinous phase generally has anaverage particle size of less than 1 micron, such as less than 0.5microns, or, in some cases, less than 0.15 micron.

In certain embodiments, the concentration of the resinous phase in theaqueous medium is at least 1 percent by weight, such as 2 to 60 percentby weight, based on the total weight of the aqueous dispersion. Whensuch compositions are in the form of resin concentrates, they often havea resin solids content of 20 to 60 percent by weight, based on weight ofthe aqueous dispersion.

In addition, the aqueous medium may contain a coalescing solvent. Usefulcoalescing solvents include hydrocarbons, alcohols, esters, ethers andketones. The amount of coalescing solvent, if any, is generally between0.01 and 25 percent, such as 0.05 to 5 percent by weight, based on totalweight of the aqueous medium.

A pigment composition and, if desired, various additives, such assurfactants, wetting agents or catalysts can be included in thedispersion. The pigment composition may be of the conventional typecomprising pigments, for example, iron oxides, strontium chromate,carbon black, coal dust, titanium dioxide, talc, barium sulfate, as wellas color pigments such as cadmium yellow, cadmium red, chromium yellowand the like. In certain embodiments, the electrodepositable coatingcomposition comprises a colorant that results in the production of adark-colored, such as an optically black, electrodepositable coatingcomposition. In certain embodiments, the dark-colored electrodepositablecoating composition is capable of producing a coating having a CIELAB L*value of no more than 40, such as no more than 30, or, in some cases, nomore than 20.

The pigment content of the dispersion is usually expressed as apigment-to-resin ratio. In certain embodiments, when pigment isemployed, the pigment-to-resin ratio is usually within the range of 0.02to 1:1. The other additives mentioned above are often in the dispersionin amounts of 0.01 to 3 percent by weight based on weight of resinsolids in the composition.

In certain embodiments of the present invention, the electrodepositablecoating composition is deposited onto the substrate so as to result in arelatively thin film, i.e., a dry film thickness of no more than 0.5mils (12.7 microns), in some cases no more than 0.2 mils (5.1 microns).Such compositions may be applied to the metal substrate using anysuitable apparatus, such as, for example, one of the methods and/orapparatus described in one or more of United States Published PatentApplication Nos. 2006/0032751A1; 2006/0032748A1; 2006/0049062A1;2006/0051512A1, and 2006/0051511A1.

It has been surprisingly discovered that it is possible to produce metalarticles coated with a multi-component composite coating comprising (i)a dark-colored zinc-rich primer coating and (ii) a dark-coloredelectrodeposited coating deposited over at least a portion of thezinc-rich primer coating, which can exhibit excellent adhesion andcorrosion resistance properties, even when relatively low filmthicknesses are used. As used herein, the team “dark-colored zinc-richprimer coating” refers to a dark-colored coating deposited from adark-colored zinc-rich primer composition. As used herein, the term“dark-colored electrodeposited coating” refers to a dark-colored coatingdeposited, by an electrodeposition process, from an aqueous dark-coloredelectrodepositable composition. As used herein, when it is stated that acoating is “deposited over” another coating, it is meant encompassscenarios where the coating is applied directly to the other coating,with no intervening coating layers being present, as well as situationswhere an intervening coating layer separates the two coatings. Incertain embodiments of the present invention, however, the dark-coloredelectrodeposited coating is deposited directly over at least a portionof the dark-colored zinc-rich primer, with no intervening coating layersbeing present.

In certain embodiments, therefore, the present invention is directed tometal articles at least partially coated with a multi-componentcomposite coating comprising: (a) a dark-colored zinc-rich primercoating; and (b) a dark-colored electrodeposited coating deposited overat least a portion of the dark-colored zinc-rich primer coating,wherein, in certain embodiments, the article is resistant to corrosionwhen tested in accordance with ASTM B117 after 500 hours of exposure, insome cases after 700 hours of exposure, or, in yet other cases, after1000 hours of exposure, when the total combined dry film thickness ofthe dark-colored zinc-rich primer and the dark-colored electrodepositedcoating is 1.5 mils or less (38.1 microns), in some cases 1 mil (25.4microns) or less. As used herein, when it is stated that an article is“resistant to corrosion” it means that the portion of the article coatedwith the multi-component composite coating has no red rust visible tothe naked eye after exposure in accordance with ASTM B117 for aspecified period of time, wherein the article is placed in a chamberkept at constant temperature where it is exposed to a fine spray (fog)of a 5 percent salt solution, rinsed with water and dried. Furthermore,when it is stated in this application that an article is resistant tocorrosion “after 500 hours of exposure” it is meant that the article isresistant to corrosion when so tested for 500 hours exactly as well asarticles resistant to corrosion when so tested after a selected numberof hours greater than 500 hours, such as a selected number of hoursbetween 500 and 1000 hours. Likewise, when it is stated in thisapplication that an article is resistant to corrosion “after 700 hoursof exposure” or “after 1000 hours of exposure” it is meant that thearticle is resistant to corrosion when so tested for 700 hours or 1000hours exactly as well as articles resistant to corrosion when so testedafter a selected number of hours greater than 700 hours or 1000 hours.

It has also been found that such multi-component composite coatingsadhere to each other and to metal substrates. Adhesion, for purposes ofthe present invention, is measured using a Crosshatch adhesion testwherein, using a multi-blade cutter (commercially available from Paul N.Gardner Co., Inc.), a coated substrate is scribed twice (at 90° angle),making sure the blades cut through all coating layers into thesubstrate. Coating adhesion is measured using Nichiban L-24 tape (fourpulls at 90°). Four purposes of the present invention, a coating isconsidered to “adhere to a metal substrate” if at least 80%, in somecases, 90% or more, of the coating adheres to the substrate after thistest.

By successfully employing a dark-colored zinc-rich primer coating incombination with a dark-colored electrodeposited coating (in certainembodiments the difference in L* value between the zinc-rich primercoating and the electrodeposited coating is no more than 40, such as nomore than 30, or, in some cases, no more than 25 units), the presentinvention can, in many cases, overcome problems associated with theunsightly “touch points” previously described. In particular, whencoated parts with “touch points” are separated from each other such thatat least some of a dark-colored electrodeposited coating is removed fromthe part at or around the touch point, the zinc-rich primer coating,which is also dark-colored, may not be particularly noticeable, unlikeas would be the case if a light, silver-colored, zinc-rich primercoating (as is common) had been deposited under a dark-coloredelectrodeposited coating (as is common).

As will be appreciated, the coated articles described herein may alsoinclude a decorative and/or protective topcoating applied over thedark-colored zinc-rich primer or the multi-component composite coatingspreviously described. Such topcoatings may be deposited from anycomposition of the type conventionally used in automotive OEMcompositions, automotive refinish compositions, industrial coatings,architectural coatings, electrocoatings, powder coatings, coil coatings,and aerospace coatings applications. Such compositions typically includefilm-forming resins, such as, for example, the materials described inU.S. Pat. No. 6,913,830 at col. 3, line 15 to col. 5, line 8, the citedportion of which being incorporated herein by reference. Such coatingcompositions may be applied using any conventional coating technique andutilizing conditions that will be easily determinable by those skilledin the art.

The present invention is also directed to methods for providing metalarticles that comprise a surface that is resistant to corrosion whentested in accordance with ASTM B117 after 500 hours of exposure. Thesemethods comprise: (a) depositing a dark-colored zinc-rich primer coatingover at least a portion of the surface, wherein the dark-coloredzinc-rich primer coating is deposited from a dark-colored zinc-richprimer composition comprising: (i) dark-colored zinc flakes present inthe composition in an amount of at least 25 percent by weight, based onthe total solids weight of the composition, and (ii) a binder formedfrom a titanate; and (b) electrodepositing a dark-colored coating overat least a portion of the dark-colored zinc-rich primer coating, whereinthe total combined dry film thickness of the dark-colored zinc-richprimer and the dark-colored electrodeposited coating is no more than 1.5mils (38.1 microns).

As should also be apparent from the foregoing description, the presentinvention is also directed to metal articles at least partially coatedwith a multi-component composite coating comprising: (a) a dark-coloredzinc-rich primer coating; and (b) a dark-colored electrodepositedcoating deposited over at least a portion of the dark-colored zinc-richprimer coating, wherein the total combined dry film thickness of thedark-colored zinc-rich primer and the dark-colored electrodepositedcoating is no more than 1.5 mils (38.1 microns) and the articles areresistant to corrosion when tested in accordance with ASTM B117 after500 hours of exposure.

Illustrating the invention are the following examples that are not to beconsidered as limiting the invention to their details. All parts andpercentages in the examples, as well as throughout the specification,are by weight unless otherwise indicated.

EXAMPLES Example 1

Charge 2 and 3 from Table 1 were premixed together then added withagitation over a 5 minute period into Charge 1 in a round bottom flaskfitted with an agitation blade, a condenser, a distillate trap, andcontinuous nitrogen feed. After 30 minutes the temperature was raiseduntil distillation occurred. After 24 grams of distillate was removed,Charge 4 was added. The resulting material was amber in color and waspourable at room temperature.

TABLE 1 Charge # Material Amount (grams) 1 Tyzor ® TnBT¹ 200 2 DeionizedWater 7.1 3 MACOL ® 98B² 94.6 4 Solvent Blend 24 24% benzyl alcohol 23%toluene 24% MIBK 24% SOLVESSO ® 100³  5% n-butanol ¹Tetra-n-butyltitanate commercially available from E.I. duPont de Nemours and Co.²Bis-phenol A-ethylene oxide diol commercially available from BASF.³Commercially available from Exxon Chemicals America.

Example 2

Charge 1 from Table 2 was blended with Charge 4 and half of Charge 5until homogeneous. Charge 3 was then added under agitation. The mixturewas heated to 120° F. and held for 15 minutes. Charge 2 was added slowlyunder agitation until well incorporated and free of lumps. The remainderof Charge 5 was added and mixed for one hour.

TABLE 2 Charge # Material Amount (grams) 1 Binder of Example 1 75.77 2Zinc Dust SF7⁴ 204.75 3 M-P-A 

 4020 X⁵ 3.50 4 Ethyl Cellulose N-200⁶ 2.72 5 Solvent Blend 77.00 24%benzyl alcohol 23% toluene 24% MIBK 24% SOLVESSO ® 100  5% n-butanol⁴Zinc powder having an average particle size of 2.5 to 4.5 microns,commercially available from U.S. Zinc. ⁵Rheology additive commerciallyavailable from Elementis Specialties, Inc. ⁶Commercially available fromHercules Co.

Example 3

Charge 1 from Table 3 was blended with Charge 2 and the mixture blendedunder agitation until the reaction was complete as evidenced by themixture becoming clear. Charge 5 and half of Charge 6 were added andblended until homogeneous and Charge 5 was completely dissolved. Charge3 was then added under agitation. The mixture was heated to 120° F. andheld for 15 minutes. Charge 4 was added slowly under agitation untilwell incorporated and free of lumps. The remainder of Charge 5 was addedand mixed for one hour.

TABLE 3 Charge # Material Amount (grams) 1 Tyzor ® TOT⁷ 57.00 2 MACOL ®98B 3.00 3 M-P-A 

 4020 X 2.37 4 Zinc Dust SF7 179.6 5 Ethyl Cellulose N-200 2.43 6Solvent Blend 84.00 24% benzyl alcohol 23% toluene 24% MIBK 24%SOLVESSO ® 100  5% n-butanol ⁷Tetra-2-ethylhexyl titanate commerciallyavailable from E.I. duPont de Nemours and Co.

Example 4

Charge 1 from Table 4 was blended with Charge 2 and the mixture blendedunder agitation until the reaction was complete as evidenced by themixture becoming clear. Charge 3 was added and stirred for 15 minutes.Charge 4 and then Charge 5 were added slowly under agitation until wellincorporated and free of lumps. Charge 6 was then added and mixed forone hour.

TABLE 4 Charge # Material Amount (grams) 1 Tyzor ® TOT 57.00 2 MACOL ®98B 3.00 3 BYK ®-410⁸ 1.86 4 Zinc Dust SF7 170.60 5 STAPA ® 4 ZnSn15⁹10.00 6 Solvent Blend 30.00 24% benzyl alcohol 23% toluene 24% MIBK 24%SOLVESSO ® 100  5% n-butanol ⁸Rheological additive commerciallyavailable from BYK-Chemie. ⁹Zinc/tin alloy flake paste commerciallyavailable from Eckhart-Werke.

Comparative Example C1

Charge 1 from Table 5 was blended with Charge 2 and the mixture blendedunder agitation until the reaction was complete as evidenced by themixture becoming clear. Charge 5 and half of Charge 6 were added andblended until homogeneous and Charge 5 was completely dissolved. Charge3 was then added under agitation. The mixture was heated to 120° F. andheld for 15 minutes. Charge 4 was added slowly under agitation untilwell incorporated and free of lumps. The remainder of Charge 5 was addedand mixed for one hour.

TABLE 5 Charge # Material Amount (grams) 1 Tyzor ® TOT 62.2 2 MACOL ®98B 3.27 3 M-P-A 

 4020 X 2.00 4 STAPA ® 4 ZnAl 7¹⁰ 146.70 5 Ethyl Cellulose N-200 2.00 6Solvent Blend 69.00 24% benzyl alcohol 23% toluene 24% MIBK 24%SOLVESSO ® 100  5% n-butanol ¹⁰Zinc/Aluminum alloy flake pastecommercially available from Eckhart-Werke.

Examples 5-11

In Examples 5-11 of Table 6, the effect of organic modification orhybridization of titanate materials is demonstrated. For examples 5through 11, the materials were blended by mechanical stirring at 25° C.until the reaction was complete as evidenced by a clear, homogeneousproduct. For examples 7 through 11, the mixtures were turbid and cloudyat first and became clear after approximately one hour of reaction time.All were fluid at room temperature.

TABLE 6 5 6 7 8 9 10 11 Example (grams) (grams) (grams) (grams) (grams)(grams) (grams) TYZOR ® TOT 10.0 — — — — — 11.43 TYZOR ® BTP¹¹ — 10.012.0 13.3 11.7 10.0 — MACOL ® 98B — — 0.4 1.0 1.5 3.0 — TERATHANE ®1000¹² 0.4 Solvent Blend of 1.0 1.0 2.0 2.0 2.0 3.0 1.0 Example 1¹¹n-butyl polytitanate commercially available from E. I. DuPont deNemours and Co. ¹²Polytetramethylene ether glycol, commerciallyavailable from INVISTA.

Application and Testing

The compositions of Examples 2, 3, 4, and C1 were applied to clean, sandblasted bolts by a dip spin method in a basket with a radius of 4 cm ata speed of 350 rpm for 15 seconds. The bolts were then baked at 200° C.for 20 minutes. In addition, the compositions were applied to clean coldrolled steel panels by drawdown bar method, and baked at 200° C. for 20minutes. The resulting film thickness was approximately 8 microns.Subsequently, the coated bolts were topcoated by electrodeposition withPowercron 6100XP (black cationic Bisphenol A epoxy based electrocoatcommercially available from PPG Industries, Inc.) for a total primerplus topcoat film thickness of approximately 16 microns, as measuredusing in accordance with ASTM B244 using a FISHERSCOPE® MMSthicknessmeter, as described above. Similarly, each primer coated steelpanel was topcoated with electrocoat over half of its surface area. Theelectrocoat was cured by baking at 180° C. for 30 minutes.

The bolts were mounted on plastic panels and placed in a salt spraycabinet compliant with ASTM B117 standard. They were tested in sets often bolts for each example. The point of failure was defined as thenumber of hours of exposure required to generate the visible appearanceof any red rust spots on more than two of the ten bolts in the set.

Adhesion testing was done by crosshatch as described above. Crosshatchwas tested on primer only as well as primer plus electrocoated topcoaton the flat steel panels described above.

The products of examples 5 through 11 were applied to flat, clean coldrolled steel panels by conventional drawdown method then baked at 200°C. for 20 minutes. The resulting dry film thickness was approximately4-5 microns. The resulting films were evaluated for film integrityvisual inspection, thumbnail scratching, rubbing with an acetone soakedrag, and visual assessment of the extent of film cracking when examinedby Scanning Electron Microscope (SEM) at 500× magnification.

Results are set forth in Tables 7 and 8

TABLE 7 Example 1 5 6 7 Appearance Smooth, dull powdery, rough powdery,slightly rough powdery, very cloudy Thumbnail no scratch very easy veryeasy easy Scratch Acetone 100 rubs had rubbed off rubbed off 5 rubsthrough soaked rag rub no effect easily easily to metal 500x (SEM) nocracks, powdery, no powdery, no mud cracks with cracking continuouscontinuous film continuous large gaps and appearance film film flaking500X Crosshatch no loss (100% complete loss complete loss no loss (100%Adhesion adhesion) adhesion) Example 8 9 10 11 Appearance smooth,smooth, clear smooth, clear smooth, dull slightly cloudy Thumbnail easyDifficult no scratch difficult Scratch Acetone soaked 100 rubs has 100rubs has no 100 rubs has 100 rubs has no rag rub no effect effect noeffect effect 500x (SEM) more less cracking, Very little very similar to8 cracking continuous, very narrow cracking, appearance less crackinggaps, no flaking narrow gaps, 500X with narrower (vs 8) mostly gaps, nocontinuous, flaking (vs 7) no flaking (vs 9) Crosshatch no loss no loss(100% no loss (100% no loss (100% Adhesion (100% adhesion) adhesion)adhesion) adhesion)

TABLE 8 Example 2 3 4 C1 Salt Spray 500 500 700 50 (Hours) CrosshatchAdhesion no loss no loss no loss complete loss Primer only CrosshatchAdhesion no loss no loss no loss complete loss Primer plus Electrocoat

Examples 12-14

In Examples 12-14 of Table 9, the effect of modification orhybridization of titanate materials with a silicon-based polymer isdemonstrated. For examples 13 and 14, the mixtures requiredapproximately 8 hours to react and become clear. All were fluid at roomtemperature.

TABLE 9 Example 12 (grams) 13 (grams) 14 (grams) TYZOR ® TOT 10.0  10.0 10.0  Dow Corning ® 840 Resin¹³ — 1.0 — SILIKOFTAL ® HTT¹⁴ — — 0.6Solvent Blend of Example 1 1.0 1.0 1.0 ¹³Silanol functional siliconeresin available from Dow Corning. ¹⁴Polyester silicone resin availablefrom Degussa.

The products of examples 12 through 14 were applied to flat, clean coldrolled steel panels by conventional drawdown method then baked at 200°C. for 20 minutes. The resulting dry film thickness was approximately4-5 microns. The resulting films were evaluated for film integrityvisual inspection, thumbnail scratching, rubbing with an acetone soakedrag, and visual assessment of the extent of film cracking when examinedby Scanning Electron Microscope (SEM) at 500× magnification. Results areset forth in Table 10.

TABLE 10 Example 12 13 14 Appearance brown, rough, Clear, smooth Clear,smooth powdery Thumbnail Scratch very easy difficult difficult Acetonesoaked rag through in 30 100 rubs 100 rubs rub rubs no effect no effect500x (SEM) severe mud less mud more cracking cracking, large crackingand continuous, less appearance 500X gaps and some small gaps crackingversus flaking versus 12 13 Crosshatch no loss (100% no loss (100% noloss (100% Adhesion adhesion) adhesion) adhesion)

Examples 15-17

Examples 15 and 17 were prepared from the ingredients set forth in Table11.

TABLE 11 Example Charge Example 15 Example 17 # Material Amount (grams)Amount (grams) 1 Tyzor ® TOT 2916 433 2 MACOL ® 98B 154 23 3 BYK-410 486 4 Zinc Dust SF7 9187 — 5 Zinc 8¹⁵ — 1241 6a Ethyl Cellulose N-200 124— 7 Benzyl Alcohol — 55 8 n-Butanol — 110.8 6 Solvent Blend 1184 36 24%benzyl alcohol 23% toluene 24% MIBK 24% SOLVESSO ® 100  5% n-butanol¹⁵Zinc flake paste in mineral spirits available from Eckart-America.

Example 15 was prepared in a manner similar to Example 3. Charge 1 fromTable 11 was blended with Charge 2 and the mixture blended underagitation until the reaction was complete as evidenced by the mixturebecoming clear. Charge 6a and half of charge 6 were added and blendeduntil homogeneous and Charge 6a was completely dissolved. Charge 3 wasthen added under agitation. The mixture was then heated to 120° F. andheld for 15 minutes. Charge 4 was added slowly under agitation untilwell incorporated and free of lumps. The remainder of Charge 6 was addedand mixed for one hour.

Example 17 was prepared in a manner similar to Example C1. Charge 1 fromTable 11 was blended with Charge 2 and the mixture blended underagitation until the reaction was complete as evidenced by the mixturebecoming clear. Charge 3 was then added under agitation followed byCharges 6, then 5, then 7, then 8. Agitation was continued for 30minutes.

Example 16 was prepared by processing 1700 grams of the compositionprepared in Example 15 in a media mill (Chicago Boiler L-3-J) which wascharged with 2400 grams of 1.7-2.4 millimeter ceramic zirconium media.This was milled at 90° F. at 2400 rpm for three hours. The materialturned from a dark gray color to a very silvery color, indicating theformation of non-spherical zinc particles.

Application and Testing of Examples 15-17

The compositions of Examples 15, 16, and 17 were applied to flat, clean,zinc-phosphated cold rolled steel panels by conventional drawdown methodand then baked at 200° C. for 20 minutes. The resulting dry filmthickness was approximately 6-8 microns. Subsequently, the coated panelswere topcoated by electrodeposition with Powercron XP (black cationicBisphenol A epoxy based electrocoat, commercially available from PPGIndustries, Inc. according to the manufacturer instructions for a totalprimer plus topcoat film thickness of approximately 15-17 microns, asmeasured in accordance with ASTM B244 using a FISHERSCOPE® MMSthicknessmeter, as described above. Similarly, each primer coated steelpanel was topcoated with electrocoat over half of its surface area. Theelectrocoat was cured by baking at 180° C. for 30 minutes.

The resulting panels were placed in a salt spray cabinet compliant withASTM B117 standard. Adhesion testing was done by crosshatch as describedabove. Crosshatch was tested on primer only as well as primer pluselectrocoat. Results are set forth in Table 12.

The SEM images of FIGS. 1 to 3 show that the milling process used inExample 16 produced non-spherical particles with significantly differentshape from the commercially available flakes of Example 17. It is alsoclear that the coating produced from the composition of Example 16 had amore porous surface than the coating produced from the composition ofExample 17.

TABLE 12 Example 15 16 17 Salt Spray (hours) 500 1000 336 Red rust spotsNo red rust Severe blisters No blisters No blisters 800 Red rust spotsCrosshatch Adhesion no loss no loss complete loss Primer only CrosshatchAdhesion no loss no loss complete loss Primer plus Electrocoat

Examples 18-20

Examples 18 and 19 were prepared from the ingredients set forth in Table13.

TABLE 13 Example(s) 18 19 Material Weight (grams) Weight (grams) Tyzor ®TOT 464.3 534.0 Tyzor ® BTP 111.7 132.0 MACOL ® 98B 24.7 28.4 BenzylAlcohol 40.0 45.1 n-Butanol 118.0 118.6 2-Ethylhexanol 39.3 83.1Solvesso 100 80.0 Silquest A187 13.0 15.0 Benton SD2 13.0 15.0 Zinc DustSF7 1179.1 — Black Zinc Z2031 — 1314.1 Oleic Acid 2.6 — BYK-410 5.0 5.8

Example 18 was prepared in a manner similar to Example 15 by mixing theingredients in order. 1700 grams of the compositions was then processedin a manner like Example 16.

Example 19 was prepared by mixing the ingredients in order anddispersing with a Cowles dispersion blade for 1 hour.

Example 20 was prepared by mixing 565.0 parts by weight of the productof Example 18 with 550.0 parts by weight of the product of Example 19and dispersing with a Cowles dispersion blade for 1 hour.

Application and Testing of Examples 18-20

The compositions of Examples 18, 19, and 20 were applied to flat, clean,zinc-phosphated cold rolled steel panels by conventional drawdown methodand then baked at 200° C. for 20 minutes. After thickness and colormeasurement, the panels were then topcoated by electrodeposition withPowercron XP (black cationic Bisphenol A epoxy based electrocoat,commercially available from PPG Industries, Inc.) according to themanufacturer instructions. The electrocoat was cured by baking at 180°C. for 30 minutes.

The resulting panels were placed in a salt spray cabinet compliant withASTM B117 standard. Adhesion testing was performed by using a 5 toothcrosshatch tester with 2 mm spacing and subsequent tape adhesiontesting. Results are set forth in Table 14 and are expressed as percentloss of the topcoat.

TABLE 14 Example 18 19 20 Zinc Rich Primer film thickness¹⁶ 0.32 mil.0.29 mil. 0.35 mil. Crosshatch adhesion <5% loss <5% loss <5% loss ZincRich Primer film thickness¹⁶ 0.79 mil. 0.81 mil. 0.76 mil. Crosshatchadhesion 70% loss <5% loss 20% loss L* value¹⁷ 68 32 52 ¹⁶As measured inaccordance with ASTM B244 using a FISHERSCOPE ® MMS thicknessmeter.¹⁷Measured at an angle of 45° using an X-Rite MA-68 available fromX-Rite, Incorporated, Grandville, Mich.

It will be appreciated by those skilled in the art that changes could bemade to the embodiments described above without departing from the broadinventive concept thereof. It is understood, therefore, that thisinvention is not limited to the particular embodiments disclosed, but itis intended to cover modifications which are within the spirit and scopeof the invention, as defined by the appended claims.

We claim:
 1. A coating composition comprising: (a) dark-colored zincparticles present in an amount of 85 percent by weight to 95 percent byweight based on the dry weight of the composition; and (b) a binderformed from a titanate and/or a partial hydrolysate thereof; wherein thebinder excludes silicon, the coating composition is substantially freeof zinc alloy particles, and the coating composition produces a coatinghaving a CIELAB L* value of no more than
 60. 2. The coating compositionaccording to claim 1, wherein the coating composition produces a coatinghaving a CIELAB L* value of no more than
 40. 3. The coating compositionaccording to claim 1, wherein the dark-colored zinc particles comprisegenerally spherical particles having an average particle size of no morethan 20 microns.
 4. The coating composition according to claim 1,wherein the dark-colored zinc particles comprise zinc powder having anaverage particle size of from 2 microns to 10 microns.
 5. The coatingcomposition according to claim 1, wherein the dark-colored zincparticles comprise zinc flakes.
 6. The coating composition according toclaim 5, wherein the dark-colored zinc flakes comprise black zincflakes.
 7. The coating composition according to claim 1, wherein thebinder further comprises a polyfunctional polymer comprising functionalgroups reactive with alkoxy groups of the titanate and/or the partialhydrolysate thereof.
 8. The coating composition according to claim 7,wherein the polyfunctional polymer comprises a polyhydroxy compound. 9.The coating composition according to claim 8, wherein the polyhydroxycompound is formed from reactants comprising (i) a polyol comprising anaromatic group and (ii) an alkylene oxide.
 10. The coating compositionaccording to claim 9, wherein a ratio of the polyol to the alkyleneoxide ranges from 1:1 to 1:10.
 11. The coating composition according toclaim 1, wherein the dark-colored zinc particles are dispersed in thebinder.
 12. A coating formed from a coating composition comprising: (a)dark-colored zinc particles present in an amount of 85 percent by weightto 95 percent by weight based on the dry weight of the composition; and(b) a binder formed from a titanate and/or a partial hydrolysatethereof; wherein the binder excludes silicon, the coating issubstantially free of zinc alloy particles, and the coating has a CIELABL* value of no more than 60; and wherein after application to asubstrate and after curing, the coating has a dry film thickness of atleast 0.5 mils.
 13. A metal article at least partially coated with amulti-component composite coating comprising: (a) a coating formed fromthe coating composition according to claim 1; and (b) a dark-coloredelectrodeposited coating deposited over a least a portion of the coatingformed from the coating composition, wherein the article is resistant tocorrosion after 500 hours of exposure when the total combined dry filmthickness of the coating formed from the coating composition and theelectrodeposited coating is no more than 1.5 mils.
 14. The metal articleof claim 13, wherein the article is a small part.